1. Field of the Invention
This invention relates to an electrode having an active material borne on a support having a three-dimensional network structure having interconnected spaces, at least the surface of the three-dimensional network skeleton being formed of a metal, especially aluminum. The electrode is useful as a positive electrode in secondary cells, especially secondary lithium cells and secondary lithium ion cells.
2. Prior Art
Positive electrode materials commonly used in prior art secondary lithium cells and secondary lithium ion cells include electrode supports in the form of metal thin plates such as stainless steel thin plates and aluminum thin plates, having an active material borne thereon. Commonly used among the active materials for the positive electrodes of secondary lithium cells are manganese dioxide, cobalt oxide, and titanium sulfide. Such an active material is blended with a binder together with an electrically conductive agent such as graphite and carbon to form an active material paste which is coated to a support as mentioned above to form a positive electrode. The positive electrode is laid on a lithium base negative electrode through a separator. The assembly, optionally after spirally wound, is impregnated with a non-aqueous electrolyte solution between the positive and negative electrodes to construct a secondary lithium cell.
In a secondary lithium ion cell, the positive electrodes is composed of lithium-metal complex oxide such as LiCoO.sub.2 carried on aluminum sheet and the negative electrode is composed of graphite carbon carried on copper sheet.
Such secondary lithium cells and secondary lithium ion cells have been used in practice although there is a need for further improvements in repeatable charge-discharge cycles, discharge electric capacity and electric power.
These cell performance factors can be increased by improving positive electrode materials. Prior art positive electrodes have active materials borne on supports in the form of thin plates of metals such as stainless steel and aluminum. All these electrode supports are not well adherent to active materials such as manganese dioxide, cobalt oxide, titanium sulfide and LiCoO.sub.2. The active materials are then susceptible to uneven deterioration, resulting in less charge-discharge cycle. If the amounts of the binder and conductive agent are increased in order to improve adhesion and conductivity, there is an accompanying lowering of discharge electric capacity and electric power. It will then be possible to improve such factors of secondary lithium cells and secondary lithium ion cells as repeatable charge-discharge cycle, discharge electric capacity and electric power by reducing the amounts of the binder and conductive agent in the positive electrode and improving the adhesion between the electrode support and the active material.